The present invention concerns improving the performance of lead acid storage batteries.
So far, lead acid storage batteries each comprised a stack of a positive plate or plates and a negative plate or plates with a separator plates or plates located therebetween. Used to this end where separators provided with glass mats, now generally referred to as a planar type of separators. Another type of separators, recently introduced in the art, have been made of such synthetic resins as polyethylene. Owing to their thinness, the polyethylene separators have the merits of being lower in electrical resistance and better in oxidation resistance than the conventional separators.
In use, the polyethylene separator, shown at 1 in FIG. 5, is longitudinally folded together with a glass mat 2 pre-laminated thereon, defining an envelope. The envelope is then joined together at its both edges 3 by welding or mechanical seals. However, if the glass mat should extend to the welds 3, welding or mechanical sealing would be unfeasible. For this reason, a glass mat smaller in width than the welds 3 of the separator, i.e. a glass mat having a width such that its widthwise edges do not reach the welds 3 is now used in combination with the separator 1. In FIG. 5, reference numeral 4 stands for a negative plate enclosed in the enveloped separator 1 and 5 stands for a positive plate.
With such a narrow glass mat, however, the positive plate 5 would be curved into contact with the polyethylene separator as depicted in FIG. 6, while the lead acid storage battery is used under severe conditions, deteriorating due to oxidation. At this portion shown at IS, there will be a short-circuit between the positive and negative plates 5 and 4.
With the foregoing in mind, the present invention have been accomplished to extend the service life of a lead acid storage battery constructed with an enveloped separator made of polyethylene or other synthetic resin.